[Bug 161528] New: Sorting/threading is broken for some messages (with option "Thread Messages")

[Thomas Friedrichsmeier]

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http://bugs.kde.org/show_bug.cgi?id=161528         
           Summary: Sorting/threading is broken for some messages (with
                    option "Thread Messages")
           Product: kmail
           Version: 1.9.9
          Platform: Debian testing
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: NOR
         Component: general
        AssignedTo: kdepim-bugs kde org
        ReportedBy: thomas.friedrichsmeier ruhr-uni-bochum de


Version:           1.9.9 (using KDE 3.5.9)
Installed from:    Debian testing/unstable Packages

This report shows some similarities to bug #139860 (but I did not import the mails in question), and bug #157209 (but this one only occurs in conjunction with the "Thread Messages") option.

Problem:
Some mails keep jumping to the top of the folder. The mails in question were all sent via bugs.launchpad.net. All start have a subject starting with "[Bug 123456]". Not all mails from bugs.launchpad.net are affected, but most are. Looking at the messages sources I fail to make out any pattern.

The behavior on those mails is absolutely weird:
1) If I sort the folder according to a new criterion, the messages are correctly sorted, where they should belong.
2) Now I switch to another folder, and then back to the one containing the messages. I scroll all the way up in the message list - the messages are sitting on top again.
3) I move a mail or two out of the folder. The strange messages jump back into place.
4) Repeat step 2 with the same result.
5) This effect is independent on both sort order and sort criterion. I.e. whatever sorting is used, these messages come out on top when switching to the folder.
6) The effect disappears when the "Thread Messages" option is turned off. The "Thread Messages also by subject" option does not make any difference with respect to the bug. Switching either option on / off has the *temporary* effect of bringing the messages back to a sensible place. If "Thread Messages" is on, step 2 applies again.
7) All mails in question are shown as top-level mails when "Thread Messages" is on, even though many are part of threads. When toggling the "Thread Messages" option off, then on, the messages are temporarily threaded correctly. After step 2, they are all shown as top-level mails again. For this symptom, changing the sorting (see steps 1&5) has no effect (messages are sorted correctly, but remain non-threaded).